Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium (e.g., glass, fabric, metal, or other objects) as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (i.e., a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a toner image. Note that the toner image may not be visible to the naked eye depending on the composition of the toner particles (e.g., clear toner).
After the latent image is developed into a toner image on the photoreceptor, a suitable receiver is brought into juxtaposition with the toner image. A suitable electric field is applied to transfer the toner particles of the toner image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (i.e., “fuse”) the print image to the receiver. Plural print images (e.g., separation images of different colors) can be overlaid on the receiver before fusing to form a multi-color print image on the receiver.
Contact fusing systems consist of a heated surface where the image and the support media is pressed against until the toner is sufficiently melted to adhere to the support media. The heated fusing surface can be roller or a heated fusing belt. The media and toner are pressed against the fuser surface with either a pressure roller or pressure belt. This roller or belt can be heated or un-heated.
For printing systems where the toner used does not include additives (e.g., release wax) to prevent adhesion of the toner to the fuser surface, a release fluid (e.g., an oil) is typically applied to the fuser surface prior to the media being fused. With printing systems that print on cut sheets of media, an interframe gap separates consecutive sheets. During this interframe gap some of the release fluid applied to the fusing surface will transfer to the pressure roller surface. In many printing systems, a contact skive is used to strip the media from the pressure roller. In such cases, any release fluid that transfers to the pressure roller can be skived by the contact skive and collect on its surface. The release fluid on the skive surface can then transfer to the back side of subsequent sheets of media. This can cause objectionable artifacts, particularly when printing in a duplex (i.e., double-sided) print mode. In this case, any release fluid which transfers to the back side of the substrate in the fusing subsystem can wet the imaging surface when the second side image is being printed by the imaging module. The release fluid on the imaging surface can then cause the printed density to be higher or lower in the corresponding image areas, which can produce undesirable image artifacts. Such artifacts can persist for many sheets of media until the release fluid is removed from the imaging surface. Drops of release fluid on the surface of the media can also cause differential gloss artifacts, or can transfer to adjacent pieces of media in the output tray producing visible surface artifacts, even in a single-sided printing mode.
There remains a need for a stripping mechanism for a fuser apparatus which effective strips the receiver medium from the fuser roller without causing the receiver medium to be contaminated with differential levels of release agent.